<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        ul {
            list-style: none;
        }

        /* 
        固定定位完全脱离标准流 
        固定定位一定要写上宽高除非有内容撑开
        */
        .top {
            height: 44px;
            background: url(./images/top.png) center no-repeat;
            position: fixed;
            top: 0;
            left: 50%;
            width: 1002px;
            transform: translateX(-50%);


        }

        .box {
            width: 1002px;
            margin: 44px auto;
        }
        /* 固定定位和浏览器窗口位置，不和父级元素有关 */
        .ad-l,
        .ad-r {
            position: fixed;
            top: 300px;

        }

        .ad-l {
            left: 0;
        }

        .ad-r {
            right: 0;
        }
    </style>
</head>

<body>
    <div class="top">
    </div>
    <div class="ad-l"> <img src="./images/ad-l.png" alt=""></div>
    <div class="ad-r"> <img src="./images/ad-r.png" alt=""></div>
    <div class="box">
        <img src="./images/box.png" alt="">
    </div>
</body>

</html>